1. Field of the Invention
The invention relates to systems and methods for controlling an operating temperature of a catalyst of a vehicle exhaust system.
2. Background Discussion
Carbon Monoxide (CO) tailpipe emissions may be difficult to control on some hybrid electric vehicles when the engine power command is large. Such aggressive driving situations expose the exhaust system's catalyst to high exhaust gas temperatures and may cause the engine subsystem controller to activate catalyst over-temperature protection measures, which enrich the air-fuel mixture. On aggressive drive cycles where the wheel power, and therefore the engine power command, is large, rich air-fuel ratios may be required to protect the catalyst. This may cause the engine to produce CO in excess of the catalyst's capability to reform it.
Exhaust gas temperature is generally proportional to engine power. Catalyst temperature may be greater than exhaust temperature due to the exothermic reactions taking place in the catalyst. Engine power above a threshold may lead to catalyst temperatures above desired operating temperatures. This may trigger air-fuel enrichment for catalyst protection, which may lead to unacceptable CO emissions.